The present invention relates to a pneumatic tire having tread blocks provided in the side wall with grooves, whereby performances on the snowy and icy roads and noise generation and wear resistance on normal roads are well improved in good balance.
According to the recent intensification in regulations for using spiked tires, the use of studless tires has been increased. Although the studless tires have no spikes, they have superior performances on the snowy and icy roads to the normal tires due to improvements in properties of the tread rubber at low temperature.
On the other hand, as the studless tires have more opportunity to be used on normal roads as well as on snowy and icy roads, it is necessary for the studless tires to upgrade the traveling properties by improving both the noise generating property and wear resistance, as well as its performance on snowy and icy roads.
Concerning these tire performances, it is known that:
(a) block type tread patterns can enhance performances on snowy and icy roads but are inferior in low noise performance;
(b) in the block type tread patterns, an increase in the ratio of the grooved area to the total area of the ground contacting face improves performance on snowy roads, but reduces the performance on icy or icebound roads;
(c) in the block type tread patterns, an increase in the number of sipes provided on the block improves the performances on snowy and icy roads, but heightens the noise level and accordingly lowers the low noise performance;
(d) on the other hand, rib type tread patterns are superior in low noise performance, but are inferior in their performance on snowy and icy roads; and
(e) in the rib type tread patterns, by reducing the number of sipes formed on the rib, the low noise performance is improved, but the performances on snowy and icy roads are reduced.
Thus, the performances on snowy and icy roads and the low noise performance and wear resistance on normal roads could not be satisfied simultaneously, and the performances on snowy and icy roads should be considered as different performances.
It is therefore, an object of the present invention to provide a pneumatic tire, in which the performances on snowy and icy roads and the low noise performance and wear resistance on normal roads are improved in good balance.